square feet

The One Big Happy in today’s feed:

Ruthie takes square foot to be Adj + N, so interpreted as ‘a foot that is square’; takes foot to denote the bodypart (rather than the unit of linear measure); and takes square to denote the shape of a square (rather than a square itself). In fact, square foot (in general, square M, where M denotes a unit of linear measure) is an idiomatic phrase denoting the area of a square that is one foot on each side (that is, as denoting the area of a foot square).

Now, whether human feet are round (or, more accurately, oval) or rectangular (that is to say, squarish) is a question open for discussion.